Weakly-Correlated nature of ferromagnetism in nonsymmorphic CrO2revealed by bulk-sensitive soft-X-ray ARPES

Chromium dioxide CrO2belongs to a class of materials called ferromagnetic half-metals, whosepeculiar aspect is that they act as a metal in one spin orientation and as a semiconductor or insulator in theopposite one. Despite numerous experimental and theoretical studies motivated by technologicallyimportant applications of this material in spintronics, its fundamental properties such as momentum-resolved electron dispersions and the Fermi surface have so far remained experimentally inaccessiblebecause of metastability of its surface, which instantly reduces to amorphous Cr2O3. In this work, wedemonstrate that direct access to the native electronic structure of CrO2can be achieved with soft-x-rayangle-resolved photoemission spectroscopy whose large probing depth penetrates through the Cr2O3layer.For the first time, the electronic dispersions and Fermi surface of CrO2are measured, which arefundamental prerequisites to solve the long debate on the nature of electronic correlations in this material.Since density functional theory augmented by a relatively weak local Coulomb repulsion gives anexhaustive description of our spectroscopic data, we rule out strong-coupling theories of CrO2. Crucial forthe correct interpretation of our experimental data in terms of the valence-band dispersions is theunderstanding of a nontrivial spectral response of CrO2caused by interference effects in the photoemissionprocess originating from the nonsymmorphic space group of the rutile crystal structure of CrO2.